Nitrate removal from groundwater using solid-phase denitrification process without inoculating with external microorganisms

Denitrification of groundwater was studied using a laboratory-scale reactor packed with biodegradable snack ware served as both carbon source and biofilm support for microorganisms. The complete removal of 50 mg/L of nitrate-nitrogen was achieved in a 23-day-old reactor with 2.1 h of hydraulic retention time without inoculating with any external microorganisms, which indicates that indigenous microorganisms in groundwater proliferate readily and result in stable biofilm formation onto biodegradable snack ware. Accumulation of nitrite and nitrate residue was detected when hydraulic retention time was lower than 2.1 h. The breakthrough of nitrate-nitrogen up to over 10 mg/L in the effluent water was observed with nitrate removal efficiency reducing to about 75 % when hydraulic retention time was lowered to 1.4 h. The highest rate of denitrification was observed with 1.5 h of hydraulic retention time. Dissolved organic carbon concentration in the effluent water ranged between 10 and 20 mg/L during the stable operation of the reactor, and nitrite-nitrogen concentration was never higher than 0.09 mg/L. Considering its relatively low price and high denitrification rate, biodegradable snack ware can become a good alternative for denitrification proces